1. Field of the Invention
The present invention relates generally to apparatus for hoisting and, more particularly, to apparatus for safely lowering and raising a sublance into and out of a basic oxygen furnace (BOF) vessel.
2. Description of the Prior Art
Heretofore, a number of systems have been introduced for manipulating various equipment, e.g., oxygen blow lances and the like, relative to a BOF vessel. These systems include for lowering and raising the equipment into and out of the vessel and normally also include means for transporting the systems to and from a "ready" position located above the BOF vessel. Typical examples of such systems are found in U.S. Pat. No. 2,822,163 to McFeaters; U.S. Pat. No. 3,022,990 to McFeaters et al.; U.S. Pat. No. 3,412,989 to Penn and U.S. Pat. No. 4,198,035 to Smejkal et al. Each of these patents disclose the use of a single, reversible (usually electric) motor for lowering and raising oxygen lances into and out of a BOF vessel. Due to the magnitudes of the loads normally moved by these motors, e.g., several tons, the motors must be large and must be operated at relatively high speed in order to create the torque necessary to overcome the high inertia of the motors themselves, their drive systems and the load being hoisted. Consequently, these motors are most effectively operated at or above a critical and relatively high speed. Hence, the loads moved thereby can only be translated at relatively high speed.
U.S. Pat. No. 3,149,191 to McFeaters et al. is to a BOF system layout including an apparatus used to raise and lower an oxygen blow lance. The vertical movement of the lance is effected in a two-stage manner by operation of a single reversible electric motor. In order to raise the lance, the electric motor is operated so as to turn a winding drum in a first direction which in turn moves a cable, which is entrained over a block and tackle pulley system and whose opposite ends are attached to the top and bottom of a lance holding carriage, within a movable guide extension carriage until an upper cable anchor abuts a pulley. At this point, continued turning of the winding drum by the motor causes the movable guide extension carriage to raise within stationary guide channels until it reaches the desired elevation whereupon the motor is deactivated. To lower the lance, the direction of turning of motor is reversed and so too are the stages of the lifting operation. Furthermore, because of the block and tackle arrangement created by the pulley system, the lance moves slowest through its regions of highest elevation wherein the block and tackle come into play. Conversely, when the movable guide extension carriage is in its lowest position, the block and tackle arrangment is no longer a factor. Below this point, the movement of the lance holding carriage is fastest since the opposite ends of the cable are permitted to freely translate in direct relation to the turning of the winding drum. That is, there is no lost motion in the carriage translation caused by the block and tackle arrangement when the movable guide extension is in its lowest position.
In U.S. Pat. No. 3,763,704 to Blau et al. there is disclosed an oxygen lance and a sublance which are carried on the same vertically reciprocable carriage whose translation is effected by a hoist. The sublance is vertically translatable relative to the oxygen lance by a second motor and a chain system carried by the carriage. There is no mention in this reference of any preferred relative hoisting speeds of the hoist motor and the second motor.
U.S. Pat. No. 3,896,674 to Kolb discloses the use of a bath sensing probe which is raised and lowered into and out of a BOF vessel by reversible air motor. When the probe is lowered to the desired depth within the vessel, a sensor carried by the probe is caused to extend into the liquid steel bath through operation of a double acting air cylinder.
And, U.S. Pat. No. 4,792,124 to Zonneveld teaches to raise and lower a sublance by conventional means and to also provide the sublance with a helical guide system for imparting rotation to the sublance during raising and lowering thereof.
The lance elevating systems disclosed in each of the aforenoted patents, whether they are expressly designated for lowering and raising sublances into and out of a BOF vessel (as in U.S. Pat. Nos. 3,896,674 and 4,792,124), whether they are expressly designated for lowering and raising an oxygen blow lance into and out of the BOF vessel (as in U.S. Pat. Nos. 2,822,163; 3,022,990; 3,149,191; 3,412,989 and 4,198,035), or whether they are designated for hoisting both an oxygen blow lance and a sublance (as in U.S. Pat. No. 3,763,704), fail to describe systems which effectively maximize speed and safety in hoisting a sublance into and out of a BOF vessel.
In those patents mentioned hereabove wherein there is disclosed only single motor means for lowering and raising an oxygen blow lance into and out of a BOF, the lance, which is typically of uncomplicated and rugged construction, may be lowered at relatively rapid speed from a position well above the BOF to its desired elevation within the BOF. If the lance should happen to strike the molten metal bath within the BOF upon insertion thereinto, the lance would not likely be damaged because of its inherent durability. However, if a substantially more delicate sublance (which monitors bath temperature, composition, and the like, were rapidly lowered into the bath using similar elevating equipment, the sudden and drastic thermal shock would very likely cause damage to the sublance.
In addition, in the aforenoted patents wherein there is disclosed only single motor means for hoisting a sublance into and out of a BOF, there is provided no means for maximizing hoisting speed through a non-critical distance above the bath in order to maximize productivity yet also enabling relatively slow hoisting speed through a critical spotting distance in order to ensure safe insertion and withdrawal of the sublance into and out of the bath.
Furthermore, in U.S. Pat. No. 3,763,704 which includes means for hoisting both an oxygen blow lance and a sublance into and out of a BOF, there is no provision of a sublance hoisting system which is independent of the oxygen lance hoisting system for controlling the hoisting speed of the sublance so as to be relatively rapid through the non-critical distance above the bath for purposes of maximizing productivity and for controlling the hoisting speed of the sublance so as to be relatively slow through the critical spotting distance in order to safely insert and withdraw the sublance from the bath. By its being carried by the blow lance carriage, the sublance hoisting system taught by U.S. Pat. No. 3,763,704 inherently exposes the sublance to potential damage if the sublance is rapidly and/or imprecisely lowered into the BOF vessel by the blow lance carriage.
It is, therefore, and object of the present invention to provide a system for hoisting a sublance into and out of a BOF vessel, such system being independent of the oxygen lance hoist system associated with the BOF, which controls the hoisting speed of the sublance so as to be relatively rapid through the non-critical distance above the molten metal bath within the BOF for purposes of maximizing productivity and further serving to control the hoisting speed of the sublance so as to be relatively slow through the critical spotting distance in order to enable safe insertion and withdrawal of the sublance into and from the bath.
It is a more particular object of the present invention to provide a two-speed hoisting system for a sublance including a first motor operatively connected with a planetary gear system for enabling high speed hoisting of a sublance through the non-critical distance above the metal bath and a second motor also operatively connected with the planetary gear system for enabling low speed hoisting of the sublance through the critical spotting distance for permitting safe insertion and withdrawal of the sublance into and from the bath.
It is a further object of the present invention to provide a cable tension sensor for detecting slack in the sublance carriage support cable, such sensor being connected to apparatus for seizing the sublance carriage in the event a slack cable or a "free-fall" condition of the sublance carriage is detected.
Still other objects and advantages of the present invention will become apparent in light of the attached drawings and written description of the invention presented herebelow.